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Full text of "The manufacture and properties of iron and steel"

480                                     THE IRON INDUSTRY.
ore was the only kind used, but the supply will be exhausted in a short time and furnaces are carrying more and more hard ore, some
FIG. XXII-J.—ORE DEPOSIT OF BIRMINGHAM, ALA,; VERTICAL SECTION.
plants using it almost alone, and there is a greater proportion of limonite (brown ore).
This hard ore follows the rules that hold for soft ore, that the content of iron decreases toward the dip, but this has nothing to do with the uniformity of the -ore at right angles to the dip. The hard ore contains a considerable proportion of lime, the relative amounts of other substances being correspondingly decreased. A general average is as follows:
HARD  OEE.
Fe.....................................    37.00
SiOa...................................    13.44
CaO  ...........................V........    16.20
AI-A,.....................................      3.1S
P .,....................................      0.37
S......................................      0.07
C0a....................................     12.24
Water ..................................      0.50
These figures show that the ore is self-fluxing. This is not true of every part of the bed, for some parts give too much silica and some too much lime, but the general fact places in a different light the low content of iron. Dolomite is used quite generally in Birmingham furnaces, the average composition being as follows:
BIBMINGHAM  DOLOMITE.
Silica...................................      1.50 to 2.00
Oilde of Iron and alumina..................      1.00
Carbonate of lime..................„.......    54.00
Carbonate of magnesia..........,..........    43.00